The present invention relates to an image forming apparatus and an image forming system and, more particularly, to an image forming apparatus and an image forming system having that may perform high-speed double-sided printing.
Commonly-used double-sided printing schemes include individual double-sided printing involving sequentially subjecting a plurality of sheets to double-sided printing one at a time and high-speed double-sided printing involving subjecting a plurality of sheets to double-sided printing at high speed with at least one second sheet undergoing printing on one side between when a first side of a first sheet is printed and a second side of the first sheet is printed.
During individual double-sided printing, after one side of a single sheet has undergone printing, the sheet is inverted so that the other side of the sheet can be printed. The next sheet then undergoes printing, one side at a time. For instance, when a print job involving printing 10 (1P-10P) pages of images on five sheets is performed using individual double-sided printing, the respective pages are printed in sequence of 2P (second page), 1P (first page; completion of first sheet), 4P, 3P (completion of a second sheet), 6P, 5P (completion of a third sheet), 8P, 7P (completion of a fourth sheet); and 10P, 9P (completion of a fifth sheet).
During high-speed double-sided printing operation, a plurality of sheets are subjected to processing one after another in sequence, with a second sheet being subjected to printing during a period between when a first side of a first single sheet has finished undergoing printing when the first single sheet is inverted to undergo printing on its second side. As exemplified below, the high-speed double-sided printing sequence can be carried out in various forms according to the configuration of an apparatus and specifics of a print job.
For instance, when a print job involving printing 10 (1P-10P) pages of images on five sheets is again to be performed, respective pages are printed in sequence of “2P, 4P, 1P (printing of the first sheet ends), 3P (printing of the second sheet ends), 6P, 8P, 5P (printing of the third sheet ends), 7P (printing of the fourth sheet ends), and 10P, 9P (printing of the fifth sheet ends). In this example, one high-speed double-sided printing sequence is performed every two sheets. Specifically, the first two sheets are subjected to one high-speed double-sided printing sequence. After completion of the sequence, the next two sheets are subjected to high-speed double-sided printing sequence. The final one sheet is subjected to individual double-sided printing.
In another example, when the same print job is performed, the respective pages are subjected to printing in sequence of; for instance, “2P, 4P, 1P (completion of a first sheet); 6P, 3P (completion of a second sheet); 8P, 5P (completion of a third sheet); 10P, 7P (completion of a fourth sheet); and 9P (completion of a fifth sheet). In the example, five sheets are consecutively subjected to printing using one high-speed double-sided printing sequence.
Incidentally, in order to ensure quality of an image, the image forming apparatus generally has an operation to measure a displacement of an image forming position and a density shift and performing image quality control to correct the displacement and the shift. Image quality control is carried out when predetermined control performance conditions are fulfilled; for instance, when a given number of prints have been produced or a given period of time has passed since image quality control was previously performed.